For a purpose of measuring blood sugar levels privately at home and elsewhere, palm-size, portable blood sugar level testers are used widely. When measuring the blood sugar level with these handy-type blood sugar level testers, a biosensor which serves as an enzyme reaction field must be attached to the level tester, and then the blood must be supplied to the biosensor.
Blood contains solid component (blood cells), and it is known that the amount of blood cells influences the measurement. In order to overcome this, some methods of measurement include steps of measuring the percentage of blood-cell component (hematocrit value) in the blood, and correcting the calculated blood sugar level in accordance with the hematocrit value.
The hematocrit value can be measured, for example, by using methods disclosed in the Japanese Patent Laid-Open No. 11-118794 and the Japanese Patent Laid-Open No. 2002-55069. In each method, the hematocrit value is measured by correlation to the level of electric conductivity (resistance).
The method disclosed in the Japanese Patent Laid-Open No. 11-118794 uses a hematocrit value measuring element to measure the hematocrit value of blood. As shown in FIG. 10A and FIG. 10B, a hematocrit value measuring element 9 includes a substrate 90 formed with a pair of electrodes 91, 92 spaced from each other on the same plane, and a layer of reagent 93 covering a pair of ends of the electrodes 91, 92.
In a liquid phase such as blood, ions in the liquid serve as a carrier in electric charge transfer, and therefore in order to measure the level of electric conductivity of a liquid phase at a high accuracy, appropriate movement of the carrier is necessary between the electrodes. For this purpose, as shown in, a conceptual drawing in FIG. 11, electric lines of force between electrodes 95, 96 should desirably be uniform. In order to provide uniform electric lines of force, it is necessary that the measuring electrodes 95, 96 are opposed to each other, and that an area of the opposed surface (A2) in the electrodes 95, 96 must be greater than or equal to an area of the section (A1) of a body of an object liquid 97.
However, as clearly shown in FIG. 10A and FIG. 10B, the electrodes 91, 92 in the hematocrit measuring element 9 are spaced in the same plane, and therefore are not opposed to each other. This leads to an electric conductivity measurement based on a localized-carrier movement due to non-uniform electric lines of force. As a result, it is impossible to accurately measure the electric conductivity, nor the hematocrit value derived therefrom.
In the above method, the hematocrit value measurement is made using the hematocrit value measuring element 9, which is a separate implement from the biosensor implement which is for the measurement of blood sugar level. This poses another problem of increased cost in measurement incurred by the needs for two analyzing implements for a single measurement of the blood sugar level. Still another problem is inconvenience, i.e. the hematocrit value measurement using the hematocrit value measuring element 9 and the blood sugar level measurement using the biosensor must be made separately by replacing the hematocrit value measuring element 9 with the biosensor.
On the other hand, in the method disclosed in the Japanese Patent Laid-Open No. 2002-55069, a blood tester uses a blood sampling probe having a double-wall construction provided by an inner tube and an outer tube, and each of the inner tube and the outer tube has a tip serving as an electrode for measurement of the electric conductivity of blood.
This method is primarily for a large apparatus such as one having a sampling probe, and is not a technique applicable to a combination of a handy-type blood sugar level tester and a biosensor.